Additive manufacturing of ultrafine-grained high-strength titanium alloys

Abstract

Additive manufacturing (AM), where a part is built layer-by-layer, is a promising approach for creating near-net shapes and is challenging the dominance of conventional manufacturing processes for products with high complexity and greater material efficiency 1 . However, achieving good mechanical properties in the as-produced part, given the variation in solidification conditions including the control of defects in AM, is challenging. In particular there are limited opportunities for post processing to further control the microstructure/properties. Therefore, further metallurgical research on materials for AM is required to accelerate the maturity of AM technology for structural components. 3D-printed titanium alloys have been used in numerous applications, including the biomedical and aerospace industries. However, the 3D-printing of many conventional titanium alloys usually results in a microstructure comprised of coarse columnar grains, which often leads to undesirable anisotropic mechanical properties. In contrast to other common engineering alloys, such as aluminium, there is no commercial grain refiner, containing potent inoculants that can survive in liquid Ti, able to control microstructure effectively. To address this challenge, we have developed a novel technique for AM by using Ti-Cu alloys with a high constitutional supercooling capacity that overrides the negative effect of a high thermal gradient in the melt pool during AM. Through this approach, it is shown that an as-printed Ti-Cu alloy specimen is comprised of fully equiaxed, fine grained microstructure without any special process control or additional subsequent treatment. The new AM Ti-Cu alloys also display promising mechanical properties, compared to conventional alloys under similar processing conditions, due to the formation of an ultrafine eutectoid microstructure by taking full advantage of the high cooling rates and multiple thermal cycles in the AM process. We anticipate that this approach will be equally applicable to other eutectoid forming alloy systems. MainMetal based 3D printing or additive manufacturing (AM) is enabling mass customization of manufactured parts. The intrinsic high cooling rates and high thermal gradient in the metal AM process often leads to a very fine microstructure and a tendency towards almost exclusively columnar grains particularly in Ti-based alloys 1 . Such columnar grains in AM Ti components can cause anisotropic mechanical properties and hence are not desirable 2 . Numerous attempts to optimise the processing parameters of AM have shown that it is extremely difficult to alter the conditions such that equiaxed growth of prior β-Ti grains is promoted 3 . According to the Interdependence Theory 4 , the key factors controlling grain Affiliations

Tailored microstructures and strengthening mechanisms in an additively manufactured dual-phase high-entropy alloy via selective laser melting

“…Consequently, the nucleation events in front of the S/L interface are suppressed and columnar grains are favored. However, the ∆T CS is proportional to the Q value (Q is the growth restriction factor) [35]:…”

Microstructure and Properties of a 2.25Cr1Mo0.25V Heat‐Resistant Steel Produced by Wire Arc Additive Manufacturing

“…Additive manufacturing (AM) is also called three-dimensional printing (3D printing) and differs from traditional material reduction (machining) processing technologies [1][2][3][4]. Additive manufacturing uses an established threedimensional data model of the parts.…”

Designer alloy enables 3D printing of fine-grained metals

“…But to achieve the strict specifications needed for some applications, the microscopic structure of printed metal objects must be controlled. On page 91, Zhang et al 1 describe titaniumcopper alloys that produce practically useful microscopic structures during additive manufacturing, removing the need for subsequent treatment. The resulting materials exhibit promising combinations of mechanical properties, comparable to those of the ubiquitous structural alloy Ti-6Al-4V, produced using conventional and additive manufacturing processes.…”

“…Together, the cells' activity indicates which direction the animal is facing in at any given moment. In 2015, it emerged that fruit flies, which are much easier than mammals to study experimentally, have strikingly similar cells, called heading neurons 1 . Fisher et al 2 (page 121) and Kim et al 3 (page 126) now build on this discovery to tackle a decades-old problem: how does this type of neuron respond to the locations of landmarks in a manner that is stable enough to be reliable, but flexible enough to allow adaptation to new environments?…”

“…This causes the printed alloy to have undesirable anisotropic (direction-dependent) properties. b, Zhang et al1 report that titanium-copper alloys produced by 3D printing contain fine grains that have similar dimensions in all directions. The alloy shown here was produced using the same conditions as in a.…”